Filters for halogenated hydrocarbons (HKW) are known from the prior art. Activated carbons that act reactively are suitable for cleaning process or exhaust air. Such activated carbons are described in the documents DE 37 13 346 A1, DE 39 35 094 A1 and DE 40 03 668 A1. The prerequisites for high sorption capacity together with optimal regeneration ability are described in DD 239 947, DE 36 28 858 A1 and DE 37 31 688 A1.
Furthermore, it is known to use dealuminated zeolites adapted to the process as the sorbents, as described in DE 197 49 963 A1. The absorbed or adsorbed halogenated hydrocarbons are desorbed by heating, condensed and recovered. DE 101 18 768 A1 describes conservative regeneration with a steam carrier for a filter cartridge. Modified and/or dealuminated zeolites having a low water absorption of less than 2 percent by mass cause a reduction in the desorption temperature that conserves the sorbent and the sorbate.
In DE 10 2006 008 320 A1, a gas passage in the upper wall region of an individual filter insert is configured in such a manner that a plug flow is produced for the gases in this region, the breakthrough curves for inhalational anaesthetics being made more uniform. The anaesthetic gases used thus have “good” breakthrough curves at the upper edge of the filter insert with the hydrophobic zeolites, that is, with a steep and clear locally and chronologically determined characteristic of the transition, in that a sharp boundary is formed between the loaded and still unloaded parts of the zeolite filling. The filter system, which has a complex action, is confusing and allows best values for its chronological profile to be determined only after long-term, empirical experience in practice has been gained.
There is no shortage of tests to increase the loading of sorption beds for cleaning gas flows. In DE 43 19 327 A1, an untreated gas flow is conducted through two sorption beds successively. After the process has finished, the first sorption bed is regenerated and the flow direction is reversed so that the flow passes through the second bed first. However, the used sorbent is replaced by a freshly regenerated one in a laborious manner.
It is also known that an improvement in sorptive separation is made possible by physical difference, for example in the pore sizes and by modifications to the sorbent beds themselves. In the case of unequal gas components, as formed by the mixture portions of nitrous oxide and anaesthetic vapours in DE 197 06 806 A1, said gas components can be separated out selectively by different types of molecular screens.
In WO 2009/083275 A1, a first sorption bed with a hydrophobic molecular screen carbon is series-connected (consecutively) upstream of a second sorption bed with a hydrophobic zeolite. The two beds each form a process stage, and the sorptive flows through them in a spatially successive manner. The two stages have a common throughput parameter for the carrier gas, especially for air, and also steam for the regeneration agent during regeneration. These process variables are of course dependent on the gas pressure and temperature and on the volumetric flow of the carrier gas. The filter arrangement can operate continuously in a production or gas-cleaning system or else can be configured as a filter cartridge that is regenerated and evacuated as needed. Sorption from the carrier gas, in particular desorption into the carrier gas and distillation with saturated steam are combined with each other.
Despite the multiplicity of known filters and filter devices, anaesthetic gases in hospitals usually pass unfiltered into the open air via a central extraction system (pipeline) and contribute to environmental pollution.